commit-graph: refactor compute_topological_levels()

This patch extracts the common code used to compute topological levels
and corrected committer dates into a common routine,
compute_reachable_generation_numbers(). For ease of reading, it only
modifies compute_topological_levels() to use this new routine, leaving
compute_generation_numbers() to be modified in the next change.

This new routine dispatches to call the necessary functions to get and
set the generation number for a given commit through a vtable (the
compute_generation_info struct).

Computing the generation number itself is done in
compute_generation_from_max(), which dispatches its implementation based
on the generation version requested, or issuing a BUG() for unrecognized
generation versions. This does not use a vtable because the logic
depends only on the generation number version, not where the data is
being loaded from or being stored to. This is a subtle point that will
make more sense in a future change that modifies the in-memory
generation values instead of just preparing values for writing to a
commit-graph file.

This change looks like it adds a lot of new code. However, two upcoming
changes will be quite small due to the work being done in this change.

Co-authored-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/commit-graph.c b/commit-graph.c
index c11b59f28b3164cee21ab972088c32082d8f5bb6..4356c8c1f4b08f82e8864ed5112ded7ccac4909b 100644 (file)
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1446,24 +1446,52 @@ static void close_reachable(struct write_commit_graph_context *ctx)
        stop_progress(&ctx->progress);
 }
 
-static void compute_topological_levels(struct write_commit_graph_context *ctx)
+struct compute_generation_info {
+       struct repository *r;
+       struct packed_commit_list *commits;
+       struct progress *progress;
+       int progress_cnt;
+
+       timestamp_t (*get_generation)(struct commit *c, void *data);
+       void (*set_generation)(struct commit *c, timestamp_t gen, void *data);
+       void *data;
+};
+
+static timestamp_t compute_generation_from_max(struct commit *c,
+                                              timestamp_t max_gen,
+                                              int generation_version)
+{
+       switch (generation_version) {
+       case 1: /* topological levels */
+               if (max_gen > GENERATION_NUMBER_V1_MAX - 1)
+                       max_gen = GENERATION_NUMBER_V1_MAX - 1;
+               return max_gen + 1;
+
+       case 2: /* corrected commit date */
+               if (c->date && c->date > max_gen)
+                       max_gen = c->date - 1;
+               return max_gen + 1;
+
+       default:
+               BUG("attempting unimplemented version");
+       }
+}
+
+static void compute_reachable_generation_numbers(
+                       struct compute_generation_info *info,
+                       int generation_version)
 {
        int i;
        struct commit_list *list = NULL;
 
-       if (ctx->report_progress)
-               ctx->progress = start_delayed_progress(
-                                       _("Computing commit graph topological levels"),
-                                       ctx->commits.nr);
-       for (i = 0; i < ctx->commits.nr; i++) {
-               struct commit *c = ctx->commits.list[i];
-               uint32_t level;
-
-               repo_parse_commit(ctx->r, c);
-               level = *topo_level_slab_at(ctx->topo_levels, c);
+       for (i = 0; i < info->commits->nr; i++) {
+               struct commit *c = info->commits->list[i];
+               timestamp_t gen;
+               repo_parse_commit(info->r, c);
+               gen = info->get_generation(c, info->data);
+               display_progress(info->progress, info->progress_cnt + 1);
 
-               display_progress(ctx->progress, i + 1);
-               if (level != GENERATION_NUMBER_ZERO)
+               if (gen != GENERATION_NUMBER_ZERO && gen != GENERATION_NUMBER_INFINITY)
                        continue;
 
                commit_list_insert(c, &list);
@@ -1471,31 +1499,63 @@ static void compute_topological_levels(struct write_commit_graph_context *ctx)
                        struct commit *current = list->item;
                        struct commit_list *parent;
                        int all_parents_computed = 1;
-                       uint32_t max_level = 0;
+                       uint32_t max_gen = 0;
 
                        for (parent = current->parents; parent; parent = parent->next) {
-                               repo_parse_commit(ctx->r, parent->item);
-                               level = *topo_level_slab_at(ctx->topo_levels, parent->item);
+                               repo_parse_commit(info->r, parent->item);
+                               gen = info->get_generation(parent->item, info->data);
 
-                               if (level == GENERATION_NUMBER_ZERO) {
+                               if (gen == GENERATION_NUMBER_ZERO) {
                                        all_parents_computed = 0;
                                        commit_list_insert(parent->item, &list);
                                        break;
                                }
 
-                               if (level > max_level)
-                                       max_level = level;
+                               if (gen > max_gen)
+                                       max_gen = gen;
                        }
 
                        if (all_parents_computed) {
                                pop_commit(&list);
-
-                               if (max_level > GENERATION_NUMBER_V1_MAX - 1)
-                                       max_level = GENERATION_NUMBER_V1_MAX - 1;
-                               *topo_level_slab_at(ctx->topo_levels, current) = max_level + 1;
+                               gen = compute_generation_from_max(
+                                               current, max_gen,
+                                               generation_version);
+                               info->set_generation(current, gen, info->data);
                        }
                }
        }
+}
+
+static timestamp_t get_topo_level(struct commit *c, void *data)
+{
+       struct write_commit_graph_context *ctx = data;
+       return *topo_level_slab_at(ctx->topo_levels, c);
+}
+
+static void set_topo_level(struct commit *c, timestamp_t t, void *data)
+{
+       struct write_commit_graph_context *ctx = data;
+       *topo_level_slab_at(ctx->topo_levels, c) = (uint32_t)t;
+}
+
+static void compute_topological_levels(struct write_commit_graph_context *ctx)
+{
+       struct compute_generation_info info = {
+               .r = ctx->r,
+               .commits = &ctx->commits,
+               .get_generation = get_topo_level,
+               .set_generation = set_topo_level,
+               .data = ctx,
+       };
+
+       if (ctx->report_progress)
+               info.progress = ctx->progress
+                             = start_delayed_progress(
+                                       _("Computing commit graph topological levels"),
+                                       ctx->commits.nr);
+
+       compute_reachable_generation_numbers(&info, 1);
+
        stop_progress(&ctx->progress);
 }